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Merge pull request #483 from sir-gon/feature/frequency_queries
Feature/frequency queries
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‎docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries-solution-notes.md

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# [Dictionaries and Hashmaps: Frequency Queries](https://www.hackerrank.com/challenges/frequency-queries)
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- Difficulty: `#medium`
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- Category: `#ProblemSolvingIntermediate` `#DictionariesAndHashmaps`
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## First solution
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The first solution is based on the idea of ​​storing the values
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​​of insert and delete operations in a dictionary.
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For the "select" operation, a search loop is made to find the expected frequency,
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which in the best case is cut off when the value is found,
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but in the worst case it goes through the entire dictionary.
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## Optimized solution
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The optimized solution tries to reduce the worst case problem above,
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reducing the select operation to direct access to the expected frequency.
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To achieve this, it is necessary to maintain an "inverted" dictionary
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where the frequency values ​​are the keys and the values ​​of each element
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are stored in a list of values ​​that have the same frequency.
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To maintain this structure, any operation that alters the data (insert, delete),
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must update "in which frequency group" the element will be.
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This solution transfers the cost of the search to the data update operations.

‎docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries.md

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# [Dictionaries and Hashmaps: Frequency Queries](https://www.hackerrank.com/challenges/frequency-queries)
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- Difficulty: `#medium`
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- Category: `#ProblemSolvingIntermediate`
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- Category: `#ProblemSolvingIntermediate` `#DictionariesAndHashmaps`
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You are given queries. Each query is of the form two integers described below:
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‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries.js renamed to ‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries_bruteforce.js

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/**
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* @link Problem definition [[docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries.md]]
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* @see Solution Notes: [[docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries-solution-notes.md]]
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*/
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// Complete the freqQuery function below.
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export function freqQuery(queries) {
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const result = [];
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const dataMap = {};
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const __DELETE__ = 2;
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const __SELECT__ = 3;
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const __NOT_FOUND__ = 0;
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const __FOUND__ = 1;
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queries.forEach((query) => {
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const [operation, data] = query;
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case __DELETE__:
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dataMap[data] = Math.max(0, current - 1);
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break;
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case __SELECT__:
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for (const [key, value] of Object.entries(dataMap)) {
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console.log(key, value);
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if (value === data) {
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result.push(1);
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break;
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}
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}
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if (result.length === 0) {
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result.push(0);
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case __SELECT__: {
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const uniqueDatavalues = new Set(Object.values(dataMap));
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if (uniqueDatavalues.has(data)) {
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result.push(__FOUND__);
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} else {
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result.push(__NOT_FOUND__);
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}
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break;
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}
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default:
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throw new Error('Invalid operation');
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}

‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries_bruteforce.test.js

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import { describe, expect, it } from '@jest/globals';
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import { logger as console } from '../../../logger.js';
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import { freqQuery } from './frequency_queries_bruteforce.js';
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import SMALL_TEST_CASES from './frequency_queries_testcases.json';
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describe('frequency_queries', () => {
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it('freqQuery test cases', () => {
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expect.assertions(4);
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SMALL_TEST_CASES.forEach((value) => {
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const answer = freqQuery(value.input);
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console.debug(`freqQuery(${value.input}) solution found: ${answer}`);
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expect(answer).toStrictEqual(value.expected);
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});
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});
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it('freqQuery border case', () => {
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expect.assertions(1);
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expect(() => {
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freqQuery([[4, 1]]);
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}).toThrow('Invalid operation');
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});
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});

‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries_optimized.js

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/**
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* @link Problem definition [[docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries.md]]
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* @see Solution Notes: [[docs/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency-queries-solution-notes.md]]
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*/
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export function updateFrequency(frequencyMap, data, currentFreq, newFreq) {
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const freqMap = frequencyMap;
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if (newFreq > 0) {
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if (freqMap?.[newFreq]) {
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freqMap[newFreq].push(data);
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} else {
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freqMap[newFreq] = [data];
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}
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}
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if (freqMap?.[currentFreq]) {
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freqMap[currentFreq] = freqMap[currentFreq].filter((f) => f !== data);
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if (freqMap[currentFreq].length === 0) {
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delete freqMap?.[currentFreq];
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}
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}
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return freqMap;
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}
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export function freqQuery(queries) {
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const result = [];
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const dataMap = {};
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const freqMap = {};
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const __INITIAL__ = 0;
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const __INSERT__ = 1;
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const __DELETE__ = 2;
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const __SELECT__ = 3;
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const __NOT_FOUND__ = 0;
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const __FOUND__ = 1;
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queries.forEach((query) => {
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const [operation, data] = query;
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const currentFreq = dataMap?.[data] ?? __INITIAL__;
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let newFreq = currentFreq + 1;
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switch (operation) {
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case __INSERT__:
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// map of values
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dataMap[data] = currentFreq + 1;
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// map of frequencies
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newFreq = currentFreq + 1;
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break;
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case __DELETE__:
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// map of values
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dataMap[data] = Math.max(0, currentFreq - 1);
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// map of frequencies
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newFreq = currentFreq - 1;
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break;
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case __SELECT__: {
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if (freqMap?.[data]) {
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result.push(__FOUND__);
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} else {
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result.push(__NOT_FOUND__);
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}
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break;
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}
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default:
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throw new Error('Invalid operation');
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}
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if (operation === __INSERT__ || operation === __DELETE__) {
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updateFrequency(freqMap, data, currentFreq, newFreq);
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}
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});
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return result;
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}
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export default { freqQuery };

‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries.test.js renamed to ‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries_optimized.test.js

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import { describe, expect, it } from '@jest/globals';
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import { logger as console } from '../../../logger.js';
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import { freqQuery } from './frequency_queries.js';
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const TEST_CASES = [
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{
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title: 'Sample Test Case 0',
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input: [
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[1, 5],
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[1, 6],
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[3, 2],
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[1, 10],
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[1, 10],
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[1, 6],
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[2, 5],
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[3, 2]
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],
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expected: [0, 1]
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}
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];
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import { freqQuery } from './frequency_queries_optimized.js';
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import TEST_CASES from './frequency_queries_testcases.json';
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describe('frequency_queries', () => {
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it('freqQuery test cases', () => {
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expect.assertions(1);
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expect.assertions(4);
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TEST_CASES.forEach((value) => {
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const answer = freqQuery(value.input);
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console.debug(`checkMagazine(${value.input}) solution found: ${answer}`);
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console.debug(`freqQuery(${value.input}) solution found: ${answer}`);
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expect(answer).toStrictEqual(value.expected);
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});

‎src/hackerrank/interview_preparation_kit/dictionaries_and_hashmaps/frequency_queries_testcases.json

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[
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{
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"title": "Sample Test Case 0",
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"input": [
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[1, 5],
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[1, 6],
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[3, 2],
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[1, 10],
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[1, 10],
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[1, 6],
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[2, 5],
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[3, 2]
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],
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"expected": [0, 1]
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},
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{
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"title": "Sample Test Case 1",
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"input": [
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[3, 4],
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[2, 1003],
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[1, 16],
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[3, 1]
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],
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"expected": [0, 1]
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},
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{
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"title": "Sample Test Case 2",
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"input": [
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[1, 3],
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[2, 3],
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[3, 2],
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[1, 4],
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[1, 5],
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[1, 5],
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[1, 4],
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[3, 2],
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[2, 4],
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[3, 2]
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],
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"expected": [0, 1, 1]
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},
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{
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"title": "Sample Test Case 3",
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"input": [
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[1, 3],
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[1, 38],
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[2, 1],
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[1, 16],
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[2, 1],
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[2, 2],
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[1, 64],
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[1, 84],
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[3, 1],
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[1, 100],
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[1, 10],
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[2, 2],
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[2, 1],
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[1, 67],
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[2, 2],
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[3, 1],
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[1, 99],
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[1, 32],
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[1, 58],
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[3, 2]
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],
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"expected": [1, 1, 0]
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}
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]

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